Uniform conductors

The resistance R of a uniform conductor is directly proportional to its length b and inversely proportional to its cross-sectional areaM. Thus... 

This equation is applicable to all conductors, electronic or electrolytic, and for uniform conductors of any cross section, not necessarily rectangular. 

There are three thermoelectric phenomena that result from correlation between propagation of heat through a conductor and displacement of the current carriers in the conductor. The Seebeck effect (Ref 1) consists of formation of an electric current in an electrical circuit formed by two dissimilar conductors if the contacts between the conductors are held at different temperatures. A reverse phenomenon, the Peltier effect (Ref 2), consists of formation of a temperature difference between the contacts in a circuit of this type if an electric current is created in the circuit by an external current source to which the circuit is connected. W. Thomson (Lord Kelvin), who explained both effects (Refs. 3,4), predicted and experimentally confirmed the existence of another thermoelectric phenomenon, named the Thomson effect, which consists of absorption or release of heat in a uniform conductor with a current passing through it when a temperature gradient (positive or negative) is present along the current direction. 

For a uniform conductor the difference in the potential per unit distance may be calculated using Ohm s law. For a conductor of unit cross-section the difference in potential between two points is equal to the current density I/A, where I is the current and A the area, multiplied by the resistance I/k ... 

Voltage gradient The continuous drop in electrical potential, per unit length, along a uniform conductor or thickness of a uniform dielectric. 

The Peltier effect is a reverse one of the Seebeck effect that was discovered by the German physicist Seebeck at earlier period (1822). Seebeck discovered that a potential difference will be resulted between two connection points in a loop composed of two dissimilar metals, if the two junctions are maintained at different temperatures. Thereafter, in 1854, the English physicist Lord Kelvin (W. Thomson) was to discover that a uniform conductor with electric current passing through will suck heat up from the surrounding when there has a temperature gradient in the conductor, which is called as the Thomson effect. 

When a current of electricity flows through a uniform conductor ab, the strength or intensity of the current depends on the difference of potential between the two points a and b, and the resistance of the conductor and according to Ohm s law, it is equal to the difference of potential divided by the resistance,... 

In the most frequently used test the sample is placed between two electrodes and the voltage is increased from zero at a uniform rate until breakdown occurs. When an insulated wine is available, the voltage can be placed between the inner conductor and a conductive medium, such as an outside metallic shield or even water. 

In a d.c. system the current distribution through the cross-section of a current-canying conductor is uniform as it consists of only the resistance. In an a.c. system the inductive effect caused by the induced-electric field causes skin and proximity effects. These effects play a complex role in determining the current distribution through the cross-section of a conductor. In an a.c. system, the inductance of a conductor varies with the depth of the conductor due to the skin effect. This inductance is further affected by the presence of another current-carrying conductor in the vicinity (the proximity effect). Thus, the impedance and the current distribution (density) through the cross-section of the conductor vaiy. Both these factors on an a.c. system tend to increase the effective... 

The generally applicable relations for a two-conductor model are derived in the following section. For simplicity, local potential uniformity is assumed for one of the two conductor phases. Relationships for the potential and current distributions, depending on assumed current density-potential functions, are derived for various applications. 

This is a transient discrete electric discharge which takes place between two conductors which are at different potentials, bridging the gap in the form of a single ionization channel (Plate 4). Based on light emission measurements of sparks with symmetrical electrode geometry, the energy is dissipated approximately uniformly along the channel. This is in contrast with asym-... 

The resistance of a length of conductor of uniform cross ection is given by... 

Now Al is the volume, between the plates, that is occupied by the uniform field X. Hence, if the energy of the charged condenser is to be regarded as associated with the field, the energy density lias to be N2/8ir per unit volume. The same result may be reached for a condenser or conductor of any shape. Consider any element of volume dv in a non-uniform field. Since (2) applies to unit volume, if (2) is multiplied by dv, we may take... 

Nothing more is assumed about the temperatures, and one result of Carnot s investigation is a rigorous definition of temperature. Further, let there be a cylinder and piston, of an absolute non-conductor of heat, closed at the bottom by a perfect conductor of heat, and containing the working substance—any substance, or mixture of substances, the pressure of which is uniform in all directions at all points and is a continuous function of temperature. Finally, we have a stand formed of a perfect non-conductor of heat (Fig. 7). 

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